1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_RESOLVER_START_FUNCTION
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_PREREQFUNCTION (3)
9  - CURLOPT_RESOLVER_START_DATA (3)
10Protocol:
11  - All
12Added-in: 7.59.0
13---
14
15# NAME
16
17CURLOPT_RESOLVER_START_FUNCTION - callback called before a new name resolve is started
18
19# SYNOPSIS
20
21~~~c
22#include <curl/curl.h>
23
24int resolver_start_cb(void *resolver_state, void *reserved, void *userdata);
25
26CURLcode curl_easy_setopt(CURL *handle,
27                          CURLOPT_RESOLVER_START_FUNCTION,
28                          resolver_start_cb);
29~~~
30
31# DESCRIPTION
32
33Pass a pointer to your callback function, which should match the prototype
34shown above.
35
36This callback function gets called by libcurl every time before a new resolve
37request is started.
38
39*resolver_state* points to a backend-specific resolver state. Currently only
40the ares resolver backend has a resolver state. It can be used to set up any
41desired option on the ares channel before it is used, for example setting up
42socket callback options.
43
44*reserved* is reserved.
45
46*userdata* is the user pointer set with the
47CURLOPT_RESOLVER_START_DATA(3) option.
48
49The callback must return 0 on success. Returning a non-zero value causes the
50resolve to fail.
51
52# DEFAULT
53
54NULL (No callback)
55
56# %PROTOCOLS%
57
58# EXAMPLE
59
60~~~c
61static int start_cb(void *resolver_state, void *reserved,
62                    void *userdata)
63{
64  (void)reserved;
65  printf("Received resolver_state=%p userdata=%p\n",
66         resolver_state, userdata);
67  return 0;
68}
69
70int main(void)
71{
72  CURL *curl = curl_easy_init();
73  if(curl) {
74    curl_easy_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, start_cb);
75    curl_easy_setopt(curl, CURLOPT_RESOLVER_START_DATA, curl);
76    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
77    curl_easy_perform(curl);
78    curl_easy_cleanup(curl);
79  }
80}
81~~~
82
83# %AVAILABILITY%
84
85# RETURN VALUE
86
87Returns CURLE_OK
88